1. Field of the Invention
The present invention relates to a composition, an adhesive and an aqueous emulsion. More particularly, it pertains to a composition useful for a variety of use especially as an adhesive. An adhesive excellent in initial adhesivity, adhesive strength and water resistance which comprises said composition, and an aqueous emulsion as the material for said adhesive and the like.
2. Description of the Related Arts
Differing from the conventional aminoplast adhesive, an adhesive which comprises as principal ingredients, a water-soluble high molecular compound, an aqueous emulsion and an isocyanate compound is free from the generation of formalin and develops an extremely high adhesive strength and water resistance only by press bonding at ordinary temperature for a relatively short time and therefore, is admirably used as an adhesive for wood (refer to, for example Japanese Patent Application Laid-Open Nos. 94739/1973 and 69139/1975). There have been proposed also as the similar adhesives, an aqueous adhesive composition which comprises the emulsion of a copolymer of a hydroxyl group-containing monomer such as allyl alcohol, 2-hydroxyethyl acrylate, N-methylolacrylamide or the like and vinyl acetate or the like; and a divalent isocyanate compound (Japanese Patent Application Laid-Open No. 26346/1974) and water-resistant adhesive composition comprising a polyvinyl acetate emulsion using a polyvinyl alcohol as a dispersant (protective colloid) and a polyvalent isocyanate compound (Japanese Patent Application Laid-Open No. 33178/1991). There is reported an adhesive comprising a polymer emulsion stabilized by polyvinyl alcohol, said polymer emulsion being produced by two-stage polymerization process wherein in the first stage is produced a vinyl acetate copolymer having a glass transition temperature of 10.degree. to 40.degree. C. and in the second stage is produced a methyl methacrylate copolymer having a glass transition temperature of 50.degree. to 120.degree. C. at a ratio of the vinyl acetate copolymer to the methyl methacrylate copolymer being 10:1 to 10:6 (Japanese Patent Application Laid-Open No. 302485/1990).
Moreover, there is disclosed an aqueous emulsion usable for an adhesive comprising as the dispersoid, polystyrene, polymethyl methacrylate, polymethyl acrylate, methyl methacrylate/butadiene copolymer, polyvinyl chloride or polyvinyl acetate and as the suspending agent, polyvinyl alcohol having a mercapto group at an end thereof (Japanese Patent Application Laid-Open No. 197229/1985).
Under such circumstances, there has recently been established Japanese Industrial Standard (JIS) regarding adhesives for wood comprising an aqueous high molecular compound and an isocyanate compound.
With increase in the objects to be bonded, however, there has arisen the necessity for further enhancing the present adhesivity level as the case may be. Specifically, an adhesive is sometimes required to have higher durability as the structural adhesive or further enhanced initial adhesivity as ordinary adhesive for individual use. In the case of the latter, the versatile application of an aqueous emulsion of a vinyl acetate resin using polyvinyl alcohol (hereinafter sometimes abbreviated to "PVA") as the dispersant has enhanced initial adhesivity but has caused the problem of water resistance being insufficient.
For the requirement of high durability and/or high water resistance there have heretofore been admirably employed an aqueous emulsion of acrylic series and that of styrene/butadiene rubber (SBR). However, since in the above-mentioned aqueous emulsions has been used an anionic surfactant or a nonionc surfactant alone or in combination with each other as the dispersant at the time of emulsion polymerization, the aqueous emulsions have involved the problem that they could not develop such initial adhesivity like the aqueous emulsion of vinyl acetate resin obtained by using PVA as the dispersant and the problem of inferior operation efficiency.
It is the present state of the aforementioned conventional adhesives that in spite of their performance being recognized to some extent, an adhesive having satisfactory performance in all respects of initial adhesivity, adhesive strength and water resistance still remains undeveloped.